AK: Add kmalloc_array() to trap multiplication overflows

This pattern is no good:

    kmalloc(elements * sizeof(T));

Since it silently swallows any multiplication overflow.
This patch adds a simple kmalloc_array() that stops the program if
overflow occurs:

    kmalloc_array(elements, sizeof(T));

1 files changed, 17 insertions, 1 deletions

diff --git a/AK/kmalloc.h b/AK/kmalloc.h
index 95e886f9cd..fedfcf7b8f 100644
--- a/AK/kmalloc.h
+++ b/AK/kmalloc.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Daniel Bertalan <dani@danielbertalan.dev>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <AK/Checked.h>
+
 #if defined(KERNEL)
 #    include <Kernel/Heap/kmalloc.h>
 #else
@@ -47,3 +49,17 @@ inline size_t malloc_good_size(size_t size) { return size; }
 #endif
 
 using std::nothrow;
+
+inline void* kmalloc_array(Checked<size_t> a, Checked<size_t> b)
+{
+    auto size = a * b;
+    VERIFY(!size.has_overflow());
+    return kmalloc(size.value());
+}
+
+inline void* kmalloc_array(Checked<size_t> a, Checked<size_t> b, Checked<size_t> c)
+{
+    auto size = a * b * c;
+    VERIFY(!size.has_overflow());
+    return kmalloc(size.value());
+}